The invention pertains to oil base drilling fluids and methods of and compositions for making such fluids.
Oil base drilling fluids are well known in the art of drilling oil and/or gas wells. Generally they comprise (1) an oleaginous liquid, such as a hydrocarbon oil, a synthetic oil such as esters and ethers, and synthesized hydrocarbons such as internal olefins, alphaolefins, polyalphaolefins, and the like; (2) a viscosifier/suspension agent to keep the solids in the fluids suspended therein; (3) a weight material to impart the desired density to the fluid; and (4) other additives such as fluid loss control agents, emulsifiers, oil wetting agents, brines, and the like.
Most oil base drilling fluids are invert (water-in-oil) emulsions wherein an aqueous phase is dispersed within the oleaginous phase. The aqueous phase, which generally comprises a solution of an inorganic salt such as calcium chloride, is stabilized by one or more emulsifiers which are effective in invert emulsions. These include the various fatty acid soaps, including oxidized tall oil soaps, preferably the calcium soaps whether pre-formed or prepared in-situ in the fluid, polyamides, alkylamidoamines, imidazolines, alkyl sulfonates, fatty acyl esters, lecithin and the like. These include so-called primary emulsifiers, secondary emulsifiers. See for example the following U.S. Pat. Nos. 2,876,197; 2,994,660; 2,962,881; 2,816,073; 2,793,996; 2,588,808; 3,244,638; 4,504,276; 4,509,950; 4,776,966; and 4,374,737. As indicated, the fatty acid soaps can be prepared in-situ in the fluid by the separate addition of the fatty acid and a base, such as calcium hydroxide (lime), to the fluid.
Typically used viscosifiers/suspending agents known in the art include organophilic clays (also known as “organoclays”) and various polymers. Exemplary organoclays are set forth in the following U.S. patents, all incorporated herein by reference: U.S. Pat. Nos. 2,531,427; 2,966,506; 4,105,578; 4,208,218. U.S. Pat. No. 5,021,170 discloses mixtures of an organoclay and a sulfonated ethylene/propylene/5-phenyl-2-norborene terpolymer.
Exemplary weighting agents or weight materials include barite, galena, ilmenite, iron oxide, siderite, calcite, and the like.